The typical prior art exhaust muffler comprises a plurality of short linear tubes which are formed with arrays of perforations, louvers, apertures or the like. The tubes of the prior art muffler are supported in a generally parallel array by a plurality of transversely extending baffles. Each baffle typically will be oval or circular and will include apertures extending therethrough for receiving and supporting the tubes of the prior art muffler. The tubes and baffles typically are mounted manually relative to one another, with the baffles being disposed at predetermined spacings along the length of the respective tubes. The particular manual assembly procedure can vary significantly. In a typical process each tube will be securely connected to at least one baffle to define tube/baffle subassemblies.
The manufacture and assembly of the prior art muffler proceeds by forming a sheet of metal into a tubular configuration with a circular or oval cross section corresponding to the shape of the baffles and with a length substantially defining the length of the muffler. The subassemblies of parallel tubes and transverse baffles then are slid sequentially into the tubular outer shell, with each baffle being spot welded to the tubular shell. A second sheet of metal then is wrapped around the tubular outer shell in generally face-to-face relationship therewith. The outer wrapper is provided on the prior art muffler to dampen or eliminate shell ring. The prior art muffler is completed by mounting opposed end caps to opposed ends of the prior art muffler. The end caps each typically are provided with an aperture for defining the respective inlet and outlet of the muffler. Mufflers intended for original equipment applications typically will have a long circuitous exhaust pipe and a long circuitous tail pipe mounted respectively to the inlet and outlet. The connection of the exhaust pipe and tail pipe to the muffler typically is carried out by manually mounting the muffler and the pipes in a complex fixture and subsequently welding the pipes to the opposed ends of the muffler. Mounting brackets or hangers may also be welded to the muffler or pipes at this time.
The above described manufacturing process for the typical prior art muffler is extremely labor intensive and slow. Furthermore, the process inherently requires a substantial amount of floor space both for carrying out the many manufacturing process steps and for storing the inventory of the numerous components incorporated into the apparatus.
The prior art also includes mufflers that are formed at least in part from stamped components. The use of stamp formed components provides at least the potential for reducing the number of parts in the muffler. Some stamp formed exhaust mufflers merely consist of a pair of opposed mateable shells which are stamp formed to define a circuitous array of tubes and chambers. The movement of the exhaust gas through the circuitous array is intended to attenuate the noise associated with the flow of exhaust gas. One muffler of this general type is shown in U.S. Pat. No. 3,638,756 which issued to Thiele on Feb. 1, 1972. The two shells of the muffler shown in U.S. Pat. No. 3,638,756 are provided with mateable peripheral flanges. The flanges may be provided with complementary arrays of nestable embossments which define areas at which the opposed external shells are brazed.
Another prior art stamp formed muffler is shown in U.S. Pat. No. 4,132,286 which issued to Hasui et al. on Jan. 2, 1979. The muffler shown in U.S. Pat. No. 4,132,286 includes a pair of opposed stamp formed external shells, each of which includes a peripheral flange. The external shells shown in U.S. Pat. No. 4,132,286 each are formed to define a single outwardly extending chamber. The muffler of U.S. Pat. No. 4,132,286 further includes stamp formed internal guide pieces each of which is substantially smaller than the corresponding external shell and each of which is provided with its own peripheral flange. The muffler of U.S. Pat. No. 4,132,286 is assembled by first spot welding the internal guides to the inner surfaces of the respective external shells. The opposed external shells with the respective guides mounted thereto are then secured to one another by seam welding about the respective peripheral flanges of the external shells.
Still another prior art stamp formed muffler is shown in British Pat. Specification No. 632,013 which is directed to a muffler having a pair of stamp formed internal plates and a pair of stamp formed external shells. The internal plates and the external shells each comprise peripheral flanges extending thereabout. The internal plates of British Pat. No 632,013 are further formed to define arrays of perforated tubes therein. The muffler of British Pat. No. 632,013 is assembled by initially spot welding the internal plates to one another at their respective peripheral flanges. The peripherally spot welded internal plates are then disposed intermediate the external shells, and the external shells are securely welded to one another about their peripheral flanges.
The principal function of exhaust mufflers is to attenuate the exhaust related noise. This noise attenuation function is carried out by the particular arrangement of perforated tubes in the muffler and by the respective volumes of the chambers surrounding the tubes. As noted above, the movement of exhaust gas through the muffler also tends to create vibration of the muffler shells, with a corresponding shell noise generated by these vibrations. The prior art conventional mufflers avoided shell noise by providing a separate outer wrapper around the outer shell of the muffler. The prior art stamp formed mufflers identified above have no adequately dealt with the noises associated with shell ring.
In addition to attenuating noise, mufflers must be able to withstand the rigorous use to which they are subjected. For example, the smooth flow of exhaust gases can be altered significantly by an improperly tuned engine. In extreme instances, a badly tuned engine will create backfires where the combustion takes place external to the engine and within a portion of the exhaust system. The explosive forces associated with backfires can severely damage or destroy an exhaust muffler. As a result, some new car manufacturers in the United States require original equipment exhaust mufflers to withstand a backfire test. In particular, the exhaust muffler must maintain its structural integrity even after exposure to repeated backfires. Backfire specifications were complied with in the prior art conventional mufflers by welding the internal baffles to the outer shell at a plurality of locations around the outer shell. The prior art stamp formed mufflers generally were employed on European cars which often did not adequately address the backfire requirements associated with most new car manufacturers in the United States. Many prior art stamp formed mufflers included separated internal baffles which could be securely welded to the external shell as in the prior art conventional mufflers described above.
Several recent improvements have been made in connection with stamp formed mufflers. One such improvement is shown in U.S. Pat. No. 4,700,806 which issued to Jon Harwood on Oct. 20, 1987, and which is assigned to the Assignee of the subject invention. The muffler shown in U.S. Pat. No. 4,700,806 is able to provide a noise attenuation performance equal to or better than conventional mufflers with separate pipes and tubular outer shells. Other significant improvements relating to stamped mufflers are shown in U.S. Pat. No. 4,736,817 which issued to Jon Harwood on Apr. 12, 1988; U.S. Pat. No. 4,759,423 which issued to Jon Harwood et al. on July 26, 1988; U.S. Pat. No. 4,760,894 which issued to Jon Harwood et al. on Aug. 2, 1988; and, U.S. Pat. No. 4,765,437 which issued to Jon Harwood et al. on Aug. 23, 1988. Each of these patents to Harwood or Harwood et al. are primarily related to structural and operational improvements in the muffler. Improvements relating to the manufacture of the stamped components for incorporation into a stamped muffler are shown in copending U.S. patent application Ser. No. 259,176 which was filed by Jon W. Harwood et al. on Oct. 18, 1988. The disclosures of the various Harwood or Harwood et al. patents and pending applications are incorporated herein by reference.
The disclosures of the above referenced patents and pending applications which are assigned to the Assignee of the subject invention are directed primarily to structural and functional improvements in the muffler, and to an efficient method for stamp forming the components of the muffler. It is an object of the subject invention to provide an efficient method and apparatus for assembling the components of the muffler.
It is another object of the subject invention to provide an efficient method for assembling the mufflers that will ensure adequate structural strength for the mufflers.
It is an additional object of the subject invention to provide a process and apparatus which enables the assembly of stamp formed mufflers within a very small area.
A further object of the subject invention is to provide a process for simultaneously carrying out a plurality of manufacturing process steps on a plurality of different stamped mufflers.